1. Field of the Invention
The present invention relates to a device for testing various semiconductor components, including integrated semiconductor circuits, known as ICs (integrated circuits).
2. Description of the Background Art
After integrated semiconductor circuits have been singulated, they undergo functional verification in a test step. To this end, ICs are brought into contact with test sockets in a test device in order to test the individual components for functionality. These test devices are usually called “IC testers” or “IC handlers.”
Although the invention is described below with reference to ICs as typical semiconductor components, it is noted that the invention is not limited thereto.
Typically components are loaded into a loading area of the handler, either loose, or in plastic tubes or in metal magazines, and then are transported to the test section of the handler as a function of the loading method.
The handlers designed for handling the components contain transport devices that provide for the continuous delivery and correct orientation of the individual ICs to the test sockets by means of pneumatic, mechanical, or manual control. The test sockets include contact units with, depending on the number of contacts of the IC, up to a hundred contact pins, known as pogo pins, which are arranged to correspond to the circuit to be tested. The test sockets, in turn, are arranged on a DUT board, which is located on the outside of the handler and has electrical contact devices connecting it to a program-controlled signal generator.
The contacting takes place inside a chamber in which the semiconductor components are heated or cooled to the desired test temperature. After a certain holding time in the chamber, for the purpose of temperature equalization, the ICs are individually picked up by the holding devices that have carrier heads with vacuum pumps and that hold the components by suction. With the aid of the carrier heads, the ICs are then pressed against the contact pins of the test sockets to produce contact between the terminals of the ICs and the test socket. After the function of an integrated semiconductor circuit has been tested, the vacuum pump at the carrier heads is briefly deactivated and an air blast is activated by means of compressed air so that the IC is released from the carrier head.
During the contacting, the program-controlled signal generator transmits test signals through the test socket on the DUT board to the electronic circuits on the IC and analyzes the response signals that come back from the IC. In addition, voltage and current flow in the semiconductor circuits are tested during the course of the functional inspection. The requirements on the contact pins are very complex here. Contact pins are generally made of steel and coated with a hard material that has a low electrical resistance and high conductivity.
Experience has shown, on the one hand, that oxides, which increase the transition resistance, form on the outer surfaces of the contact pins after a few test cycles. This significantly reduces the service life of the contact pins or of the entire test socket.
On the other hand, the problem in testing ICs is that the contact areas or solder joints of an electronic component typically has a metallic material, for example tin solder or aluminum, which forms an oxide layer on its surface in air. This oxide layer is often harder than the pure metallic material. When the contact pins are pressed against the contact area, this metal oxide layer, which has a thickness of several μm, must be overcome. Conventional contact pins have an internal spring that makes it possible to exert a high normal force on the contact point of the IC with the tip of the contact pin during the tests, thus penetrating the metal oxide layer. In this process, the test pins are mechanically stressed, and in addition small quantities of metal oxide are deposited on the tips of the contact points during each test sequence.
It is precisely these deposits of metal oxide that are problematic, since they can react with the metal of the contact pins as a function of the metals, temperatures, and pressures that are present in each case. Furthermore, the tin of the solder connections can also diffuse into the contact tips, altering the metallic structure there.
Depending on whether the ICs are for use at high, low or room temperatures, the temperature in the holding chamber is set up in accordance with the test program. If the chamber is to be cooled, liquid nitrogen is used, which arrives at the chamber through separate lines. In contrast, heating of the chamber is accomplished through air, which is also used for supplying compressed air to the pneumatically driven transport devices. During testing at room temperature, contacting of the ICs takes place in an open system rather than a closed one. As a result, fresh oxygen is provided to the electronic components just before the test phase at room temperature or at high temperatures, which promotes oxide formation at the surface of the contact pins and at the surface of the contact areas or solder joints of the ICs.
Because of these circumstances, the contact pins, and hence the test sockets as a whole, wear very quickly. Replacing the contact pins is very expensive, however, since it not only requires the requisite material, but also down time in the test phase, during which the entire test device or the entire handler is idle.
Consequently, a variety of cleaning methods for the tips of the contact pins are known from current practice, such as mechanical or chemical cleaning of the contact pins, to improve the measurement reliability. However, these methods are beset by the disadvantage that the contact pins can be damaged during cleaning, or chemical residues may remain on the contact pins.
For this reason, attempts have been made to produce contact pins with a surface of metal that does not oxidize or only oxidizes minimally. To this end, metals such as gold, silver, platinum, palladium, iridium, rhenium, mercury, and osmium are used, which generally are less reactive with respect to oxygen and have advantageous physical and electrical properties. In addition, the shape of the surfaces of the contact pin tips has been varied in order to achieve the smallest possible surface, and thus to minimize the contact area between the pins and the ICs.
WO 03027689 A1 discloses a contact pin whose surface is coated with a palladium-cobalt alloy to reduce the adhesion of metal oxide deposits from the tin solder on the contact points. However, this increases the electrical resistance of these contact pins relative to those having a coating of nickel or gold.
A disadvantage of the conventional processes is that they are either time intensive or very costly on account of the use of expensive materials and manufacturing processes.